The present invention relates to machine inspection of transparent, shaped articles of manufacture such as contact lenses or intraocular lenses, for example. More specifically, the present invention relates to a novel machine inspection system for detecting defects in a lens.
Inspection devices and methods for detecting defects in an ophthalmic lens are known, some examples of which may be seen in the following patents:
U.S. Pat. No. 3,822,096 to Wilms et al on Jun. 2, 1974;
U.S. Pat. No. 5,443,152 to Davis on Aug. 22, 1995;
U.S. Pat. No. 5,574,554 to Su et al on Nov. 12, 1996; and
U.S. Pat. No. 6,301,005 to Epstein et al on Oct. 9, 2001.
The main purpose of an ophthalmic lens inspection system is to test the lens for defects such as cracking, chipping, warping, etc., which, if found, result in the lens having to be rejected and scrapped. In many prior art inspection systems, a light source is passed through the lens from one side (e.g., beneath the lens) and a camera, such as a CCD camera, is used to receive the light rays which have passed through the lens and thereby image the lens. In this method, the entire lens is lighted and seen as a bright spot to the camera while defects appear as dark spots. A computer may be used in conjunction with the camera to correlate pixels using algorithms which determine whether a lens has passed or failed inspection. This backlighting method of lens inspection is imperfect in that, by lighting the entire lens to the camera, particularly small defects tend to be overwhelmed by the high background signal and may therefore be missed by the inspection system.
In many of the prior art inspection systems which inspect hydrogel (soft) lenses, inspection is carried out while the lens is in the hydrated state. The lens is located for imaging by placing the lens in a holder with a saline or other solution. If a xe2x80x9cwet-releasexe2x80x9d method of lens release from the contact lens mold is used, a wet lens inspection is then necessary, however, this method of lens inspection has drawbacks. In many of the prior art methods of wet lens inspection, the lens must be placed in a vessel together with a quantity of solution (usually saline) wherein the lens is held during inspection. This creates problems in being able to precisely locate and hold the lens steady during imaging of the lens. This is because with the lens in a solution, it is able to freely move about in the vessel and may become off-center or ride up the wall of the vessel. If this happens, the imaging device will not be lined up correctly with the lens and will read the image received as a xe2x80x9cfailxe2x80x9d, resulting in many false-fail occurrences. Furthermore, in order for the lens to be imaged, a light source must pass through the lens which necessitates its holder, i.e., the vessel and solution, be able to correctly orient the lens and transmit light therethrough in a manner which does not distort the imaging of the lens. These factors, which must be considered when imaging a wet lens, result in added steps and cost to the manufacturing process.
In lens manufacturing systems which include a dry release of the lens from its mold, the lens may be inspected while still in the dry state. This provides the advantage of not having to keep the lens in solution during imaging which presents difficulty in correctly orienting the lens for imaging as discussed above. In many prior art inspection systems utilizing a dry lens inspection, the back-lighting method of lens inspection is used wherein the light source is directed from beneath through the lens where a camera placed above the lens picks up the light and analyzes the image for defects. While this method may provide the benefit of better control over being able to correctly orient the lens for imaging, this method still suffers from the limitations of detecting all defects using a light source which passes from beneath the lens from the convex side to the concave side thereof.
The present invention provides a lens inspection system which images a lens, preferably while the lens is in the dry state (i.e., it has not yet been hydrated), using a source of structured light which is directed at the full periphery of the lens edge. As such, the structured light travels through the lens in the same manner as a fiber optic conduit wherein the light is totally internally reflected by the lens, finally exiting the lens at the edge thereof directly opposite the point of light entry. As such, defect-free areas of the lens appear as extremely low contrast areas on the image detector. Conversely, defects in the lens cause the internally reflected light to scatter, thereby exiting the lens at the surface corresponding to the location of the defect and causing a bright, high contrast area spot on the image detector.